In the manufacture of semiconductor or electronic devices, photolithographic techniques or processes are often used. In the photolithographic or lithographic process, a circuit pattern contained on a mask or a reticle is projected or imaged onto a photosensitive substrate.
The now patterned after processing photosensitive substrate is further processed to form a semiconductor or other electronic device by well known techniques. The substrate is typically a wafer. As the feature sizes required to be printed become smaller, different techniques for imaging the features become necessary. One technique for providing an improved quality of printing of the pattern is the use of a phase shift mask or reticle. The use of a phase shift mask or reticle generally requires the exposure of the same field or area on a photosensitive substrate or wafer first with a phase shift mask and second with a trim mask. The trim mask is physically distinct from the phase shift mask and may be printed with separate exposure conditions.
Accordingly, where the photolitographic process requires exposure of the same field on a photosensitive substrate with different masks, the masks must be changed between each exposure. This change greatly reduces throughput and often creates potential alignment problems. A time consuming and potentially error prone alignment process must be done for each mask used to expose the field on the photosensitive substrate or wafer. Accordingly, there is a need for a reticle stage and method for exposing the same field with at least two different masks or reticles in a manner to increase throughput and prevent alignment or calibration problems. There will always be a decrease in throughput as the wafer is essentially exposed twice. There is a need to eliminate this loss in throughput to close to the unavoidable two exposure loss.